The present invention relates, in general, to semiconductor packages, and more particularly, to substrate-polymer interfaces of semiconductor packages.
Generally, semiconductor die are encapsulated within packages to prevent them from becoming damaged by external stresses and to provide a means for carrying electrical signals to and from the devices in the semiconductor die. Included in the repertoire of semiconductor die package types are dual-in-line packages, TAB packages, plastic quad flat packages, plastic ball grid array packages, and multichip modules. A common technique for packaging semiconductor die includes mounting them to a support, such as a leadframe, and encapsulating the semiconductor die and a portion of the leadframe within a polymer such as a mold compound.
An important aspect in packaging semiconductor die within a mold compound is preventing delamination of the mold compound from the substrate to which the semiconductor die are mounted. Typically, delamination occurs at the weakest interfaces between the mold compound and the substrate, resulting in the accumulation of moisture at the delamination sites. During high temperature process steps, e.g., solder reflow processes, the moisture vaporizes and causes the semiconductor package to crack via a phenomenon commonly referred to as a "popcorn effect."
To prevent delamination from occurring, semiconductor device manufacturers have sought ways to improve the interfacial adhesion between the polymer and the substrate. One technique for improving adhesion is to treat the substrate surface with silane. Although silane treatment improves mold compound adhesion, it is difficult to selectively deposit the silane and to control the thickness of the deposited silane. In addition, silane has a relatively short shelf-life and is susceptible to degradation during high temperature exposures such as occurs during die bond cure and wire bond processing steps. Thus, the leadframes must be treated with silane just before the encapsulation by the mold compound. Another technique for decreasing delamination is to form oxides on the substrate, e.g., cuprous or cuptic oxides on a copper leadframe. However, selectively forming oxides on the leadframe is difficult and expensive.
Accordingly, it would be advantageous to have a substrate and a method for improving interfacial adhesion between a polymer and the substrate. In addition, it would be advantageous for the substrate and the method to be simple, inexpensive, and to readily fit into standard packaging regimes.